1. Field of the Invention
This invention relates to a method of inspecting a magnetic disk such as a floppy disk, and more particularly, to a method of detecting surface defects in a magnetic disk in an inspection step of a magnetic disk manufacturing process.
2. Description of the Prior Art
When a surface defect due to fine irregularities in the magnetic layer or dust deposited on the magnetic layer exists in a magnetic disk, drop-out of information recorded on the disk can occur. Accordingly, magnetic disks having such surface defects must be rejected in the inspection step of the magnetic disk manufacturing process.
Conventionally the method of surface defect inspection comprises steps of recording a predetermined inspection signal on a randomly selected track of the magnetic disk during a first rotation of the disk; reading the inspection signal and setting a reference value for the disk during a second rotation of the disk; again reading the inspection signal, comparing the value of the read signal with the reference value and determining whether any surface defect exists based on the result of the comparison during a third rotation of the disk; and seeking for another inspection track during a fourth rotation of the disk. In accordance with the conventional method, a time corresponding to four rotations of the disk is required for inspection of one track.
The surface defect inspection must be effected on a plurality of tracks in real time, and accordingly the conventional method of surface defect inspection is disadvantageous in that the time required for inspection is long, which substantially adds to the manufacturing cost of the magnetic disk.